1. Field of the Invention
The present invention generally relates to a technique for learning reference position of a variable valve unit.
2. Description of the Related Art
In Japanese Laid-open (Kokai) Patent Application Publication No. 2005-188286, there is disclosed a variable valve mechanism in which a valve lift amount and a valve operation angle of an engine valve are continuously varied by a rotation of a control shaft, which is rotated by an actuator.
In addition, in the above published document, it is disclosed that the actuator is controlled such that the minimum valve lift amount and the minimum valve operating angle are achieved during fuel cut while a vehicle is being decelerated, and in such event, outputs of an angle sensor which detects a rotating angle of the control shaft are learned.
Incidentally, in learning the sensor output, the control shaft is rotationally driven by an actuator until the rotational motion of the control shaft is restricted by a stopper, and then the output of the angle sensor obtained when the control shaft comes in contact with the stopper is learned.
However, continuously applying the actuator torque to the control shaft with the control shaft being kept in contact with the stopper causes deflection in an angle sensor mounting unit, etc., and in turn a change in the outputs of the angle sensor occurs even though the rotation of the control shaft is being stopped, and as a result, an unpleasant problem occurs in which learning accuracy might be degraded.